Re: conditional unique index to restrict duplicates of a particular set
- From: Mark Bobak <Mark.Bobak@xxxxxxxxxxxx>
- To: "vijaysehgal21@xxxxxxxxx" <vijaysehgal21@xxxxxxxxx>, ORACLE-L <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 7 May 2014 13:50:10 +0000
You don't mention a version number.
If you're on 11g, you could create 4 new virtual columns:
Alter table feed_details (add non_p_feed_date date generated always as CASE
WHEN fed_typ!='P' THEN feed_date ELSE null END);
(not sytax checked)
Do the same for the other three columns, then do index as:
Create unique index on
feed_details(non_p_feed_type,non_p_branch_code,non_p_acc_number) compress n
nologging;
Consider the compressibility of the first 'n' columns, and replace n above,
with appropriate value.
IMHO, this looks "neater". Also, if you apply predicates to a query, for
example, if you know for a fact that you're only interested in rows where
fed_typ != 'P', then you can use these columns in your predicates, and the
index should be utilized. If you have a situation where the table is quite
large, but you're interested only in rows where fed_typ!='P', and that set of
rows is relatively small compared to the total size of the table, then this
index could be quite advantageous. By only indexes the "interesting" rows, the
index is much more cache friendly and efficient. But, those are all only
potential side effects of this technique. By creating virtual columns, and a
unique index on them, it should serve your purpose.
Hope that helps,
-Mark
From: vijay sehgal <vijaysehgal21@xxxxxxxxx<mailto:vijaysehgal21@xxxxxxxxx>>
Reply-To: "vijaysehgal21@xxxxxxxxx<mailto:vijaysehgal21@xxxxxxxxx>"
<vijaysehgal21@xxxxxxxxx<mailto:vijaysehgal21@xxxxxxxxx>>
Date: Wednesday, May 7, 2014 at 3:52 AM
To: ORACLE-L <oracle-l@xxxxxxxxxxxxx<mailto:oracle-l@xxxxxxxxxxxxx>>
Subject: conditional unique index to restrict duplicates of a particular set
Dear Experts,
I have a few questions with reference to below scenario:
Table Structure : feed_details( id_pk number,
acc_number number,
branch_code number,
feed_date date,
feed_type varchar2(1),
balance number
);
The feed_type can have three values 'I','E' and 'P'. We have to put a
conditional unique constraint on acc_number, branch_code, feed_date and
feed_type. The feed_date will have date and time will be always set to midnight.
The constraint is to be put such that duplicates of feed type 'P' should be
allowed but duplicates for 'I' and 'E' should not be allowed.
e.g. acc_number|branch_code|feed_type|feed_date
101 |10 | I | 07052014
102 |10 | E | 07052014
101 |10 | I | 07052014 -- should not be allowed
102 |10 | E | 07052014 -- should not be allowed
103 |10 | P | 07052014
103 |10 | P | 07052014
FB unique index as below would allow this to be achieved.
CREATE UNIQUE INDEX idx_feed_details
ON feed_details(CASE WHEN fed_typ!='P' THEN feed_date ELSE null END,
CASE WHEN fed_typ!='P' THEN acc_number ELSE null END,
CASE WHEN fed_typ!='P' THEN branch_code ELSE null END,
CASE WHEN fed_typ!='P' THEN feed_type ELSE null END);
1) How should we correctly measure the performance hit after his index is
created (the inserts would be concurrent from multiple java connections).
2) Since the index is only to restrict duplicates, would this index be helpful
in some other scenarios of data selection when the predicate is on these
columns.
3) any other overheads / side effects of this kind of index.
Hope the questions and scenario is clear.
Thanking you all for your time and help.
Warm Regards,
Vijay Sehgal.
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